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ExxonMobil, Georgia Tech Tout Reduced CO2, Energy Costs in Chemical Manufacturing

ExxonMobil Corp. and the Georgia Institute of Technology (Georgia Tech) said a team of scientists may have broken the code to reduce the amount of energy and carbon emissions associated with making plastics.

The research, published in the peer-reviewed Science journal, indicated that if the breakthrough were brought to industrial scale, annual global carbon dioxide (CO2) emissions could be reduced by up to 45 million tons, equivalent to the annual energy-related CO2 emissions of about five million U.S. homes. Global energy costs might decline by up to $2 billion a year.

Using a molecular-level filter, the new process relies on a form of reverse osmosis to separate para-xylene, a chemical building block for polyester and plastics, from complex hydrocarbon mixtures. Currently, commercial-scale processes rely on energy and heat to separate those molecules.

"If advanced to commercial-scale application, this technology could significantly reduce the amount of greenhouse gas emissions associated with chemical manufacturing," said ExxonMobil Research and Engineering Co.'s Vijay Swarup, vice president of research and development.

The research demonstrated that para-xylene may be separated from like chemical compounds, aka aromatics, by pressing them through a membrane that acts as a "high-tech sieve, similar to a filter with microscopic holes." Commercially practiced separations involve energy-intensive crystallization, or adsorption with distillation.

Globally, the amount of energy used in conventional separation processes for aromatics is equal to about 20 average-sized power plants. Chemical plants account for about 8% of global energy demand and about 15% of the projected growth in demand to 2040, according to ExxonMobil.

The scientists working together first developed a carbon-based membrane to separate molecules as small as a nanometer. The membrane then was incorporated into a new organic solvent reverse osmosis process, during which aromatics were pressed through the membrane, separating out para-xylene.

Researchers were led by Georgia Tech’s Ryan Lively of the School of Chemical & Biomolecular Engineering and included the university's Dong-Yeun Koh, as well as ExxonMobil's Benjamin McCool and Harry Deckman.

"In effect, we'd be using a filter with microscopic holes to do what an enormous amount of heat and energy currently do in a chemical process similar to that found in oil refining," said ExxonMobil's Mike Kerby, corporate strategic research manager.

The carbon-based membrane is said to be about 50 times more energy efficient than the current state-of-the-art membrane separation technology. Because the new membrane is made from a commercially available polymer, ExxonMobil said it has potential for commercialization and integration into industrial chemical separation processes.

Reverse-osmosis membranes already are used to desalinate seawater, consuming a fraction of the energy required by thermally driven processes. The newly developed organic solvent reverse osmosis process may to be the first to use reverse osmosis with carbon membranes to separate liquid hydrocarbons.

"By applying pressure at room temperature, the membrane is able to concentrate para-xylene from a mixture at high rates and low energy consumption relative to state-of-the-art membranes," said Lively, an assistant professor at the School of Chemical & Biomolecular Engineering. "This mixture could then be fed into a conventional thermal process for finishing, which would dramatically reduce total energy input."

The technology still faces challenges before commercialization. The membranes used in the process would need to be tested under more stressful conditions as industrial mixtures normally contain multiple organic compounds, ExxonMobil said. Researchers also have to learn to make the material consistently and demonstrate that it is able to withstand long-term industrial use.

"The implications could be enormous in terms of the amount of energy that could be saved and the emissions reduced in chemical and product manufacturing," said McCool, an advanced research associate who co-authored the research. "Our next steps are to further the fundamental understanding in the lab to help develop a plan for pilot plant-scale demonstration and, if successful, proceed to larger scale. We continue to work the fundamental science underlying this technology for broader applications in hydrocarbon separations."

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